Most discussions around wide-bandgap (WBG) power semiconductors tend to focus on individual devices. Engineers compare RDS(on), input and output charge, switching losses and efficiency, searching for the ideal SiC or GaN device for their application. But as wide-bandgap technologies mature, the package surrounding the die is increasingly determining how much of that performance can actually be used in a real system.
Because SiC and GaN devices can switch faster and operate at higher junction temperatures than conventional silicon devices, the limitations of the package become more apparent at the system level. Whether the goal is a more compact EV On-Board Charger (OBC), a higher-density front-end power supply unit (PSU) or more efficient high-voltage (> 400 V) 3-phase standard inverters and hybrid solar inverters, WBG packaging often determines how much of the semiconductor's theoretical performance can actually be converted into usable system-level performance.
Power density is about heat
The industry often defines increasing power density as delivering more power from a smaller volume. In practice, power density is frequently limited by a simple challenge: removing heat. Even if reducing the size of passive components is seen as the key to reducing converter volume, that reduction is only possible if switching frequency can be increased, and frequency can only be increased if the operating temperature does not simultaneously increase.
The low switching loss characteristic of wide bandgap devices may then be exploited, not to reduce total loss, but to increase frequency and power output without increasing total loss. Which means that extraction of heat from the semiconductor die is indeed a limiting factor.
The package, with its thermal pad, forms the bridge between the semiconductor and the cooling system. It influences thermal resistance, heat spreading capability and ultimately the maximum usable power level of the design. And while the size of the package’s thermal pad is not the complete story for heat flow, it is significant, as the total area of the thermal pad limits flow into the heat sink, regardless of the junction-to-pad thermal resistance.
Top-side cooling is gaining momentum
Traditional surface-mount power packages typically remove heat through the PCB before transferring it to a heatsink or cooling structure. A path that limits how much heat can be extracted as power levels rise, while simultaneously restricting use of the PCB for signal routing. Classic leaded through-hole packages, such as the TO-247, effectively separate thermal and electrical paths. Their large metal tab enables direct heatsink attachment, providing high current-handling capability and low thermal resistance while minimizing constraints on electrical routing.
Top-side cooled packages achieve similar thermal performance benefits while keeping the manufacturing advantages of surface-mount assembly. They create a direct thermal path from the device to a heatsink or cold plate, separating thermal management from the PCB. This enables more efficient heat extraction and greater layout flexibility, making the approach increasingly attractive as designers pursue higher power density and more compact converter designs.
Examples include advanced package technologies such as TOLT, X.PAK, QDPAK and top-side cooled copper-clip (CCPAK) variants. The benefit is straightforward: better thermal extraction creates additional electrical and thermal headroom, allowing the converter to operate at higher power levels or with reduced cooling requirements. However, top-side cooling isn't without its trade-offs. Designers need to weigh questions such as how tight the tolerance is on package height, and whether the mechanical system can apply controlled, even pressure to compress the Thermal Interface Material (TIM). In addition, TIM selection must accommodate the full range of gap widths allowed by the various tolerances. Factors that can directly affect thermal performance and long-term reliability.
Packaging is more than just thermal performance
WBG devices switch significantly faster than traditional silicon technologies, making performance more sensitive to parasitic inductance. Excess inductance can contribute to voltage overshoot, ringing, EMI challenges and reduced switching performance. Package design therefore directly influences electrical performance as well as thermal capability.
A relationship that becomes increasingly important at higher operating voltages, as minimum spacings are governed by creepage and clearance requirements. Larger spacings invariably mean longer path lengths and higher inductance. Consequently, achieving both high-voltage capability and low-inductance design presents a key packaging challenge for modern power electronics.
This is one reason why the industry continues to evolve beyond traditional package formats. Solutions such as TOLL, TOLT, X.PAK and QDPAK are designed not only to improve cooling but also to support compact layouts and lower-inductance current paths. In many modern converter designs, package choice has become an optimization exercise – balancing thermal performance, electrical parasitics, manufacturability and reliability.
Package technology as a competitive differentiator
As SiC and GaN devices continue to push the boundaries of efficiency and switching performance, the next gains in power density are increasingly being determined by what surrounds the die rather than the die itself. Thermal extraction, top-side cooling architectures, package parasitics and system integration all play a growing role in converter performance. Looking ahead, innovations such as double-sided cooling (where copper-clip is the right choice) are expected to further reduce thermal resistance and unlock even higher power densities in demanding applications. The result is a fundamental shift in industry thinking: packaging is no longer simply an implementation detail, but a critical technology layer that directly determines achievable power density, efficiency and reliability. For designers pursuing the next generation of high-density power systems, package technology may prove to be one of the most important competitive differentiators.
For more on Nexperia’s WBG portfolio, check out our Wide-bandgap semiconductors Technology Hub.